Ignition devices of the kind producing a plasma flame as distinct from conventional arc sparking plugs have typically comprised an ionizing chamber and an orifice in the chamber wall to permit a plasma flame to project out therefrom. Potential energy from a first source is applied across a gap between two electrodes, which gap usually is the width of the chamber. Typically, the potential is insufficient to cause a discharge across the gap unless the chamber is small, thereby restricting the gap. Or, if the discharge does take place, it is insufficient to develop a flame front that effectively burns unless the orifice is very small (see U.S. Pat. Nos. 3,911,307 and 3,921,605). Thus, the prior art has resorted to a third electrode of higher potential to assure a gap discharge. The three electrode devices are illustrated in U.S. Pat. Nos. 3,842,818; 3,842,819; 3,988,646; and 4,071,800.
A need exists in fuel injected stratified charge internal combustion engines for a precisely controlled combustion of the combustible mixture. The flame front must be stable and sustained to withstand the high transfer motion of inducted air which is swirled and squished in a special pattern (see U.S. Pat. Nos. 3,315,650; 3,439,656; and 3,696,798). Plasma ignition devices can be useful to a fuel injected stratified charge engine because the plasma flame front can be more stable and offers the potential for more sustained ignition. However, due to the type of plasma jet emitted by known plasma plugs, the latter is unable to provide complete and desirable combustion in light of the extremely high transfer motion that is taking place within the combustion chamber of a stratified charge engine. It would be desirable if plasma flame ignition systems could be modified to consume the fuel spray pattern more fully, but also to operate with two electrodes which offer greater design freedom and versatility in gap spacings.